Delay lines for microwave tubes

ABSTRACT

Certain UHF electron tubes using the interaction between an electromagnetic wave and an electron beam comprises a delay line made up of periodic elements having an aperture for the transit of said beam, the height of said elements decreasing at the end of the delay line to match said end to the input and/or output connections. The present invention allows to avoid the interception of a certain fraction of the beam by the element part comprised between the aperture and the edge of said element, when said part, at said end of the delay line, is reduced. The improvement relates to UHF electron tubes operating in very short wavelengths.

United States Patent Yeou [ Mar. 7, 1972 [S4] DELAY LINES FOR MICROWAVE TUBES Ta Yeou, Paris. France [30] Foreign Application Prlority Data Aug. 4, I969 France ..6926689 [52] U.S. Cl. ..333/31A, 315/16, 315/393 [51] Int. Cl. ..ll03h 7/30 [58] FieldoiSearch ..3l5/3.5,3.6,39.3;333/3l A [56] References Cited UNITED STATES PATENTS 2,966,610 l2/l960 Schmidt et a] ..3l5/3.5

2,926,280 2/l 960 Hergenrother ..3 1 5/16 3,353,l2l ll/i967 Dube ..3l5/3.5 X

FOREIGN PATENTS OR APPLICATIONS 1,050,845 2/1959 Germany ..333/3l A Primary Examiner-Herman Karl Saalbach Assistant Examiner-Saxfield Chatmon, .Ir. Attorney-Cushman. Darby & Cushman [57] ABSTRACT Certain UHF electron tubes using the interaction between an electromagnetic wave and an electron beam comprises a delay line made up of periodic elements having an aperture for the transit of said beam, the height of said elements decreasing at the end of the delay line to match said end to the input and/or output connections. The present invention allows to avoid the interception of a certain fraction of the beam by the element part comprised between the aperture and the edge of said element, when said part, at said end of the delay line, is reduced. The improvement relates to UHF electron tubes operating in very short wavelengths.

5 Claims, 7 Drawing Figures Patented March 7, 1972 Patented March 7, 1972 7 3,648,194

2 Sheets-Shae t 2 DELAY LINES FOR MICROWAVE TUBES The present invention relates to electronic tubes for generating or amplifying Ul-IFlSHF/EHF power (hereinafter generally referred to as UHF power or UHF), in which frequently use is made of the interaction between electron beam and the electric component of an electromagnetic field. In order to secure optimum interaction, it is generally advantageous to reduce the phase velocity of the wave in order to make it comparable with that of the electrons, and accordingly, for the wave to propagate, an electrical line of periodic structure conventionally referred to as a dely line, is employed.

This type of line comprises periodically disposed elements, arranged for example in a straight line and taking the form of conductive plates, discs or fingers creating electrical capacitances, between which the interacting electric field is developed and in the immediate proximity of which the electron beam is passed.

In order to improve the efficiency of interaction, it is the object to subject the beam to the strongest possible electric field and in certain embodiments the beam is in fact passed through holes formed directly in said periodic elements of the delay line at the level where the electric field is of maximum strength.

On the other hand, it is essential to effect propagation of the waves along the delay line without any risk of power reflections at the ends, in particular at the input and output connections. For this purpose, at the ends of the delay line, a progressive law in the creation of the electrical capacitances between the elements is exploited and this, by varying one of their dimensions. The result is that the dimensions of the holes formed in these elements in the aforedescribed manner, can become of the same order of magnitude as the dimension of said elements and that the metal thicknesses left between the edges of the holes and the external contours of said elements, become insufficient to cope with the dissipation of the heat created by the impact of part of the electron beam on said delay line elements. The result may be melting of the metal of which these elements are made, with consequent failure of the electronic tube.

In order to reduce the risk of this kind of failure, the designers have found it necessary to limit the number of elements having this small metal thickness and consequently to give the terminal zones of the line in which these elements have progressively varying dimensions, the shortest possible lengths thus making it a more difficult and delicate operation to achieve wave propagation without reflection.

The present invention relates to a novel design of the periodic elements in said terminal zones, such that their lengths can be freely chosen without any risk of the possibility of partial melting of the constituent elements.

More precisely, the invention relates to a delay line for cooperating with the electron beam of an UHF electron tubes said delay line comprising a plurality of conductor elements supported on a base and positioned periodically along said beam; each of said elements having an aperture crossed by said beam; a portion of said elements having a cut-out part extending from said aperture towards the edge of said element, opposite to said base, said cutout part being a slot perpendicular to said edge; said slot having an axis positioned symmetrically with respect to said aperture.

The invention will be better understood from a consideration of the attached Figures given here by way of example.

FIG. 1 illustrates one end of a known kind of delay line;

FIG. 2 illustrates an element of the main part of the line;

FIG. 3 illustrates an element of one end of said line;

FIG. 4 illustrates one end of a delay line in accordance with the invention;

FIG. 5 illustrates an element of one end of a delay line in accordance with the invention;

FIG. 6 illustrates a variant embodiment of such an element;

FIG. 7 illustrates another variant embodiment.

FIG. 1 provides an overall view of one end of a known kind of delay line. The electron-gun, constituted by an electronemissive cathode l and associated focusing arrangements such as 2, emits a beam 3 which passes along the delay line. Each periodic elements 7 contains a hole 5 whose diameter is in the order of that of the beam. The terminal elements or fingers have progressively decreasing lengths in order, as already described, to enable wave propagation to take place over the ends of the delay line without any risk of reflection.

The alignment of the holes thus defines a passage for the transit of the electron beam, and a certain proportion of said beam is intercepted by said fingers in a zone 6 located in the immediate neighborhood of each hole, even through the electron source and its focusing arrangements, as well as a directional magnetic field parallel to said passage, are adjusted precisely in order to avoid this undesirable phenomenon.

The result of this interference is the production of heat energy leading to a temperature rise which can reach a dangerous level if the distribution of this energy and its dissipation by thermal conduction towards the bases of the fingers, is nonuniform. Calculations and the results of experience agree in suggesting that it is the terminal portions 7 of each finger which is most inadequately cooled, and that this cooling depends upon the height of the finger.

FIG. 2 illustrates an element or finger of the main part of the line. The ratio of the interception height of the beam 8 to the total height 9 of the terminal part, is very much lower than unity and this guarantees good heat distribution in this portion, as well as good heat dissipation by the lateral parts 10.

FIG. 3 illustrates one of the elements or fingers of the terminal parts of the delay line. The total height here is much shorter and the ratio of the beam interception height, which is the same as in the previous case, to the height 9 of the terminal part, tends towards unity. The heat generated is no longer distributed in an adequate volume of material and its dissipation is made difficult because of the reduction of the section of the lateral parts.

FIG. 4 illustrates a delay line in accordance with the invention. At the terminal parts of the line where the lengths of the elements vary, the perforated elements are replaced by elements whose upper edge have been cut out for Ming up a slot so that the upper interception zone is avoided. This modification can be effected to all the elements of decrean'ng length or only to ones below a certain length beyond which it is considered that there is a danger of overheating. The as sembly of these openings thus constitutes a longitudinal slot parallel to the axis of the line and of the same width as the hole diameter. In the case where this width is in something like the same order as the wavelength involved, which could give rise to problems of propagation of the UHF wave, it may be ad visable to make the slot narrower than the hole diameter.

FIG. 5 illustrates an element or finger of the delay line in accordance with the invention whose the width of the slot 12 is equal to the width of the aperture I5.

FIG. 6 illustrates an element in accordance with the invention equipped with a slot 13 of smaller width than the width of the aperture 15.

FIG. 7 illustrates an element in which the slot has been prolonged into the part 14 of the elements located at the fixing end.

By way of example, in a typical application the width of a finger is 120p, its length I00 and the diameter of the hole 60 At the end of the line, 30 elements, equally spaced at p intervals, have decreasing lengths and can be given the characteristics defined in accordance with the invention.

What I claim is l. A delay line for cooperating with the electron beam of an UHF electron tube, said delay line comprising, between its two extremities, a plurality of conductor elements positioned along said beam and supported on a base on which they are perpendicularly maintained and along which they are periodically distributed, each of said elements having an aperture 2. A delay line as claimed in claim I, wherein the width of said slot is equal to a fraction of the aperture width.

'3. A delay line as claimed in claim 1 wherein the width of said slot is equal to the aperture width.

4. A delay line as claimed in claim 1 wherein said aperture is a hole.

5. A delay line as claimed in claim 1 wherein said slot extends from said edge towards said base beyond said aperture. 

1. A delay line for cooperating with the electron beam of an UHF electron tube, said delay line comprising, between its two extremities, a plurality of conductor elements positioned along said beam and supported on a base on which they are perpendicularly maintained and along which they are periodically distributed, each of said elements having an aperture crossed by said beam, those elements among said plurality of elements which are located at least in the zone of one of said extremities of said delay line having a dimension perpendicularly to said base, smaller than the dimension of the other elements of said plurality, said some elements having a cutout part extending from said aperture towards and up to the edge of said element, opposite to said base, said cutout part being a slot perpendicular to said edge, said slot having an axis positioned symmetrically with respect to said aperture.
 2. A delay line as claimed in claim 1, wherein the width of said slot is equal to a fraction of the aperture width.
 3. A delay line as claimed in claim 1 wherein the width of said slot is equal to the aperture width.
 4. A delay line as claimed in claim 1 wherein said aperture is a hole.
 5. A delay line as claimed in claim 1 wherein said slot extends from said edge towards said base beyond said aperture. 